This invention pertains to electrical connections, and more particularly relates to electrical rotary connectors.
Slip rings are used in a variety of applications to transfer electrical signals, including power signals, between components where one component rotates in relation to another component. One application where slip rings are used is in magnetic chucks to transfer power from the stationary frame of the magnetic chuck to the magnetic chuck rotating assembly. The slip ring is typically composed of a metal ring upon which a graphite material brush (and the like) rubs and transfers the signal. The metal ring or the graphite material brush rotates. FIG. 6 illustrates a typically slip ring assembly 10. The brush 12 is placed in a sleeve of a brush holder 14. The brush 10 is in electrical contact with brush connection 16 and a wire assembly 18 is connected to the brush connection 16. During operation, the brush contacts a conductive metal ring 20. A connection point 22 is attached to the ring 20 and wire leads 24 are connected to the connection point. As the ring 20 or brush 12 rotates, the brush 12 rubs against the ring 20 and signals are transferred across the brush/ring interface 26. The ring 20 and/or the brush 12 is connected to a rotating member of a device (not shown).
The operation of the slip ring is technically simple. However, there are a number of problems with slip rings in magnetic chuck applications. The brush wears down over time, which leads to degradation in the efficiency of transferring power and degradation of signal quality. Additionally, the brush and metal ring typically have high resistance, which results in power loss due to I2R heating losses. The resistance varies due to oxidation and other factors, which increases power losses and the fluctuations causes electrical noise. Additionally, the slip rings may need high levels of maintenance to remove the debris causes by the wear of the brushes and to replace the brushes. Other problems include electrical arcs that are produced as the slip ring assembly rotates. The arc, in combination with other factors, can lead to demagnetization problems with the magnetic chuck.
The invention provides brushless rotary connector for use in magnetic chuck applications and the like. The rotary connector uses a housing having a sealed metal fluid with sliding contacts capable of handling high current levels. During rotation, the fluid maintains the electrical connection between the contacts without any wear, and the use of the liquid metal as a conduction path offers an extremely low resistance connection that is constant.
The housing is mounted in a base that serves as a support for the housing and for connections to the stationary component. The rotating member of the rotary connector is connected to a ring that is attached to the rotating member of the magnetic chuck. This connector is a simple, low cost and highly reliable connector. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.